Variable resistor



April 63 c. s. DASH 3,085,218

VARIABLE RESISTOR Filed Dec. 7, 1960 INVENTOR. CARL S. DASH ATTORNEY United States Patent Ofiiice 3,085,218 Patented Apr. 9, 1963 3,085,218 VARIABLE RESISTUR Carl S. Dash, 1409 Church Road, Wyncote, Ia. Filed Dec. 7,1960, Ser. No. 74,254 4 Claims. (Cl. 338-163) The present invention relates to a variable resistor, and more particularly to a miniature variable resistor for use as a volume control in such small, compact electrical devices as hearing aids, pocket radios and the like.

With the miniaturization of electronic tubes, and the increasing use of transistors, the trend has been to making such electrical devices as radios, hearing aids and the like smaller and more compact. Such small, compact electrical devices require a miniaturization of all of the components used therein including the variable resistors used as the volume control. In fact, for use in hearing aids which are completely assembled in the ear piece of the frame of eye glasses, it is necessary to provide a variable resistor which is as small as approximately onequarter inch in diameter and three thirty-seconds of an inch in thickness. Since the standard, commercially available variable resistor comprises a large number of small parts, it has been found that it is impractical to merely reduce the size of such variable resistors to the small sized units required. Therefore, it has been found that a variable resistor of a size'for use in the small, compact electrical devices must be constructed of a minimum number of parts for ease of manufacture of the small parts, and for ease of assembling the parts.

It is an object of the present invention to provide a novel variable resistor.

It is another object of the present invention to provide a miniature variable resistor for use as the volume control in small, compact electrical devices.

It is a further object of the present invention to provide a miniature variable resistor having a minimum number of parts for ease of manufacture of the resistor.

Other objects will'appear hereinafter.

For the purpose of illustrating the invention there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a sectional view of the variable resistor of the present invention.

FIGURE 2 is a view of the variable resistor of the present invention taken along line 22 of FIGURE 1.

FIGURE 3 is a view of the variable resistor of the present invention taken along line 33 of FIGURE 1.

Referring initially to FIGURE 1, the variable resistor of the present invention is generally designated as Variable resistor 10 comprises a flat, circular base plate 12, and a cup-shaped cover 14 mounted on the base plate 12 for rotation relative thereto. The base plate 12 and the cover 14 are each of an electrical insulating material, such as a plastic. For use in small, compact electrical devices, the assembly of the cover 14 and the base plate 12 can be made as small as approximately one-quarter of an inch in diameter, and three thirtyseconds of an inch in thickness.

Base plate 12 has a pair of terminal pins 16 and 18 extending therethrough. Each of the terminal pins 16 and 18 has a fiat head 16a and 18a respectively at one end. The heads 16a and 18a of the terminal pins 16 and 18 are embedded in the inner surface 20 of the base plate 12 with the top surfaces of the 'heads 16a and 18a being flush with the inner surface 20. As shown in FIGURE 3, the terminal pins 16 and 18 are positioned adjacent the peripheral edge of the base plate 12, and are circumferentially spaced apart approximately 60.

The terminal pins 16 and 18 are made of an electrically conductive metal, and project beyond the outer surface 22 of the base plate 12.

A shaft 24 is mounted on the center of the base plate 12, and projects upwardly from the inner surface 20 of the base plate. A terminal pin 26 is integral with and projects axially from the end of the shaft 24 which is mounted on the base plate 12. The shaft tenninal pin 26 extends through the base plate 12, and projects beyond the outer surface 22 of the base plate. Shaft 24 has an annular groove 28 in its outer surface adjacent the free end thereof. The shaft 24 and its terminal pin 26 are made of an electrically conductive metal. The shaft 24 with its terminal pin 26, and the terminal pins 16 and 18 are secured to the base plate 12 such as by molding the base plate 12 directly to and around the shaft 24 and the terminal pins 16, 18 and 26.

An arcuate stripe 30 of an electrical resistance material is coated on the inner surface 20 of the base plate 12. The resistance stripe 30 extends circumferentially for approximately 300 around the inner surface 20 of the base plate 12 adjacent the outer periphery of the base plate. As shown in FIGURE 3, the ends 30a and 30b of the resistance stripe 30 are spaced apart, with one end 30a extending over and contacting the head 16a of the terminal pin 16, and the other end 30b extending over and contacting the head 18a of the terminal pin 18. Thus, the terminal pins 16 and 18 provide the terminals for the resistance stripe 30. The resistance value of the resistance stripe 30 is dependent on the width, length and thickness of the resistance stripe 30 as well as the particular composition of the resistance stripe. The resistance stripe 30 may :be coated on the base plate 12 by painting, spraying or the like.

The base plate 12 is provided with an integral stop lug 32 projecting upwardly from the inner surface 20 thereof. Stop lug 32 is positioned on the inner surface 20 of the base plate 12 adjacent the shaft 24, and on the side of the shaft 24 diametrically opposite the gap between the ends 30a and 30b of the resistance stripe 30. The stop lug 32 is of a circumferential length such that its end 32a is on the same diameter of the base plate 12 as the end 30a of the resistance stripe 30, and the end 321) of the stop lug 32 is on the same diameter of the base plate 12 as the end 30b of the resistance stripe 30.

The cover 14 has a flat top 34, and a cylindrical side 36 extending from the periphery of the top 34. The top 34 of the cover 14 has a central hole 38 therethrough. The cylindrical side 36 of the cover 14 is provided with serrations 40 on its outer surface to permit ease of rotating the cover 14. A stop lug 42 is integral with and projects downwardly from the inner surface of the top 34 of the cover 14. The stop lug 42 is substantially the same length as the side 36, and as shown in FIGURE 2 is positioned on the inner surface of the top 34 of the cover 14 adjacent the hole 33 through the top 34.

A contact 44 is secured to the inner surface of the top 34 of the cover 14. The contact 44 comprises a circular disc of a suitable electrically conductive spring metal, such as beryllium or copper. Contact 44 has a central hole 46 therethrough of a diameter corresponding to the diameter of the hole 38 through the top 34 of the cover 14. As shown in FIGURE 2, the contact 44 has an arcuate opening 48 therethrough which extends around approximately of the hole 46. The opening 48 provides the contact 44 with an arcuate contact arm 50 of a circumferential length of approximately 180. The contact arm 50 has a rounded contact point 52 bent therefrom. The contact point 52 is circumferentially positioned intermediate the ends of the contact arm 50. As shown in FIGURE 1, the contact 44 is bent along a diameter adjacent the ends of the contact arm 50 so that the contact arm Ed is at an angle with respect to the remaining portion of the contact 4.

The contact 4 t is mounted flat against the inner surface of the top 34 of the cover 14 with the contact arm extending away from the inner surface of the top 34. The contact 44 is positioned so that the contact point 52 is on the side of the hole 38 through the top 34 of the cover 14 diametrically opposite the stop lug 42, as shown in FIGURE 2. The contact 44 is secured to the cover 14 by a hollow rivet 54- of an electrically conductive metal. The rivet 54 extends through the hole 38 in the top 3 1 of the cover 14, and through the hole 46 in the contact 44. The rivet 54 has an annular flange 56 extending radially outwardly from its inner end, and an annular flange 58 extending radially outwardly from its outer end. The inner flange 5-6 of the rivet 54 overlaps the portion of the contact 44 around the hole 46 in the contact to clamp the contact 44 to the top 34 of the cover i l. The outer flange 58 of the rivet 54 extends across and is embedded in the portion of the outer surface of the top 34 of the cover 14 around the hole 38. The inner flange 56 of the rivet 54 has a portion cut away to permit the stop lug 42 of the cover 14- to project there through. The contact 44 also has a portion adjacent the central hole 46 cutaway to permit the stop lug 4 2 to project therethrough.

The assembly of the cover 14 and the contact 44 is mounted on the base plate 12 with the shaft 24 extending through the rivet 54. A C--washer 6t} fits tightly within the groove 28 in the shaft 24 to secure the cover 14 on the shaft 24. The shaft 24 is of a length so that when the cover 1 is mounted on the shaft, the base plate 12 is within and extends across the open end of the cover 14, and the contact point 52 of the contact arm 50 slidably engages the resistance stripe 3d. The contact arm 50 of the contact 4-4 extends from the contact 44 a distance such that when the cover 14 is assembled on the shaft 24, the engagement between the resistance stripe 3t? and the contact point 52 pushes the contact arm 50 back toward the top 34 of the cover 14 slightly. Since the contact arm 50 is of a spring metal and is pushed back slightly, the contact arm 50 acts as a spring to maintain proper engagement between the contact point 52 and the resistance stripe 39. The spring action of the contact arm 56 also urges the top 34- of the cover 14 away from the base plate 12 to hold the outer flange 58 of the rivet 54 in engagement with the C-washer 6%).

In the assembled condition of the variable resistor of the present invention, the shaft terminal pin 26- is electrically connected to the contact point 52 through the shaft 24, the rivet 54, and the contact 4. Thus, in the use of the variable resistor 10 of the present invention, a varying resistance is obtained between the shaft terminal pin 26 and either of the terminal pins 16 and 18 by rotating the cover 14 on the shaft 24 with respect to the base plate 12. The serrated edge it of the cover 14 permits ease of rotating the cover 14. In fact, the serrated edge 40 of the cover 14 permits the cover 14 to be rotated with respect to the base plate 12 even when the variable resistor 10 is mounted with only a portion of the periphery of the cover 1 1- exposed.

The stop lugs 32 and 42 project from the base plate 12 and the top 34 of the cover 14 respectively a distance such that the stop lugs 32 and 42 are in overlapping relation longitudinally of the shaft 24. Thus, upon rotation of the cover 14 with respect to the base plate 12, the stop lugs 32 and 42 will come into mating engagement to limit such rotation. The stop lug 42 on the cover 14 is of a circumferential length that when the end 42:: of the stop lug 42 engages the end 32a of the stop lug 32 on the base plate 12, the contact point 52 is at the end 300 of the resistance stripe 3t and when the end 42b of the stop lug 42 engages the end 32b of the stop lug 32, the contact point 52 is at the end 391) of the resistance stripe 30. Thus, the stop lugs 32 and 4-2 limit the rotation of the contact point 52 to the length of the resistance stripe 30.

The present invention may be embodied in other specific forms without departing from the'spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim:

1. A variable resistor comprising a base plate of an electrical insulating material, an arcuate resistance stripe on one surface of said base plate, terminals extending from the ends of said resistance stripe, a cover of an electrical insulating material extending over the one surface of said base plate and the resistance stripe, a shaft mounted on the base plate at the center of the arcuate path of the resistance stripe and projecting from the one surface of the base plate, said cover having a hole therethrough through which the shaft extends to support said cover for rotation with respect to said base plate, a contact of an electrically conductive metal seated against the surface of said cover facing said base plate, said contact having a contact point slidably engaging said resistance stripe, a hollow rivet of an electrically conductive metal extending through the hole in the cover and surrounding the shaft, said rivet fixedly securing the contact to the cover and slidably engaging the shaft so as to electrically connect said contact to said shaft, and a terminal for said contact secured to said shaft and extending through the base plate.

2. A variable resistor in accordance with claim 1 in which the cover is cup-shaped, and the base plate is circular with the base plate extending across the open end of the cover.

3. A variable resistor in accordance with claim 2 including a separate stop lug on each of the base plate and the cover, said stop lugs being in overlapping relation longitudinally of the shaft and being positioned so that they are engageable to limit the rotation of the contact point to the length of the resistance stripe.

4. A variable resistor in accordance with claim 3 in which the contact comprises a disc of an electrically conductive spring metal, said disc having a central hole therethrough through which the shaft extends, and an arcuate opening therethrough around a portion of said central hole, said arcuate opening providing an arcuate contact arm, said contact arm being bent adjacent its ends to extend away from the cover and toward the base plate, and the contact point being formed on said contact arm.

References Cited in the file of this patent UNITED STATES PATENTS 2,451,241 Rosentreter Oct. 12, 1948 FOREIGN PATENTS 783,782 Great Britain Oct. 2, 1957 796,931 Great Britain June 25, 1958 

1. A VARIABLE RESISTOR COMPRISING A BASE PLATE OF AN ELECTRICAL INSULATING MATERIAL, AN ARCUATE RESISTANCE STRIPE ON ONE SURFACE OF SAID BASE PLATE, TERMINALS EXTENDING FROM THE ENDS OF SAID RESISTANCE STRIPE, A COVER OF AN ELECTRICAL INSULATING MATERIAL EXTENDING OVER THE ONE SURFACE OF SAID BASE PLATE AND THE RESISTANCE STRIPE, A SHAFT MOUNTED ON THE BASE PLATE AT THE CENTER OF THE ARCUATE PATH OF THE RESISTANCE STRIPE AND PROJECTING FROM THE ONE SURFACE OF THE BASE PLATE, SAID COVER HAVING A HOLE THERETHROUGH THROUGH WHICH THE SHAFT EXTENDS TO SUPPORT SAID COVER FOR ROTATION WITH RESPECT TO SAID BASE PLATE, A CONTACT OF AN ELECTRICALLY CONDUCTIVE METAL SEATED AGAINST THE SURFACE OF SAID COVER FACING SAID BASE PLATE, SAID CONTACT HAVING A CONTACT POINT SLIDABLY ENGAGING SAID RESISTANCE STRIPE, A HOLLOW RIVET OF AN ELECTRICALLY CONDUCTIVE METAL EXTENDING THROUGH THE HOLE IN THE COVER AND SURROUNDING THE SHAFT, SAID RIVET FIXEDLY SECURING THE CONTACT TO THE COVER AND SLIDABLY ENGAGING THE SHAFT SO AS TO ELECTRICALLY CONNECT SAID CONTACT TO SAID SHAFT, AND A TERMINAL FOR SAID CONTACT SECURED TO SAID SHAFT AND EXTENDING THROUGH THE BASE PLATE. 